GENERATION RATE AND COMPOSITION OF SOLID WASTE

GENERATION RATE AND COMPOSITION OF SOLID WASTE

2.1 INTRODUCTION

The characteristics, quantities, volume and composition of solid waste generated may differ from one country to another and between urban and rural areas. It depends mainly upon the customs, climate, living conditions and economic standard of the area.

2.2 GENERATION RATE OF SOLID WASTE

Determination of the generation rate of solid waste is important to obtain data in order to determine determining the dimensions of the key elements in solid waste management. These elements include method and type of storage, type and frequency of collection, crew size, method of disposal, and degree of resource recovery.

Factors to consider for the purpose of determining the generation rate are:

1. Measures of quantities
2. Volume measurement.
3. Weight measurement

Be careful in volume measurement because you need to distinguish wastes which are compacted and loosened. Both have different weight and volume. Weight is the most accurate basis for records regardless of whether the waste is loose or compacted. Weighing can be done for instance on each vehicle and its load of wastes as it enters the disposal site using permanently installed or a portable scales. To account for changes due to seasonal or other temporal factors, the weighing should be conducted for a minimum two-week period, at either two or four intervals distributed throughout the year. A sample data collection sheet for waste measuring is shown below:

2. Statistical Analysis

It is necessary to have some statistical base for solid waste management system development. This includes placement of containers, programming the collection and allocation of vehicle type.

3. Expression of Unit Generation

In addition to knowing the source and composition of solid waste, it is important to have uniform units of expression.

1. Residential and Commercial – kilogram per capita per day (Kg/c/d)
2. Agricultural –Kilogram per hectare per year (kg/ ha/ year)

4. Methods Used to Determine Generation Rate
5. Load count analysis –basically involves counting of the individual loads over a specified time period. If possible, weighing the load will be very important.
6. Weight -volume analysis– measuring the volume of the truck and weight of each load will give ample data.

Although the technique is expensive, it is used to: draw a system boundary round the unit to be studied; identify what occurrences affect generation rates; identify the rate of generation associated with different activities using the data available; determine the quantity of waste generated, stored and collected

5. Typical Generation Rate

This is the rate found by conducting a large survey very representative for a nation, state or locality.

6. Factors Affecting Generation Rates

Factors that affect the generation rate of solid waste include:

1. Geographical location -related primarily to the different climate that can influence both the amount     generated and collection operation.
2. Season of the year
3. Frequency of collection
4. Characteristics of population e.g. low/high income, boarding
5. Extent of salvage and recycling
6. Legislation
7. Public attitude

Other factors may also affect generation rate in site specific cases for instance in a learning institution factors determining generation rate include: existence of boarding facilities, courses offered- technical courses including wood work and metal work produce more waste than business courses.

2.3 COMPOSITION OF SOLID WASTE

Composition of solid waste depends on the local factors such as time of the year or season, habits of the community, educational status, economic status, geographical location, and population size.

1. Physical Composition

Knowing the physical composition of solid waste is important for the selection and operation of equipment facilities, to assess the possibility or feasibility of energy recovery and to design disposal facilities. Its analysis may contain individual component study, moisture content study and density.

1. Chemical Composition

It is very important to study the nature and value of solid waste to plan different disposal and recovery options. These studies include the assessment of moisture content, volatility, ash content, etc. The moisture content of municipal solid wastes varies depending on composition of the waste, the season of the year, humidity and weather condition. To reduce the magnitude of errors arising from moisture change and from decomposition, analysis of the samples should be begun within two to three hours after collection. These analyses must be conducted by a reliable laboratory for instance those that have been gazette by NEMA e.g. KEBS, Government Chemist, KARI etc.

2.4. Solid Waste Storage

Type of waste with respect to its length of storage days

Waste type Length of storage days Control guide line (minimum)

Garbage                       4                                 Fly breeding

Residential rubbish   7                                 Flies, land pollution

Mixed refuse              4                                 Flies

Street sweeping         7                                 Unsightliness

Dead animals                         1                                  Flies, animal diseases

Special waste                         1                                  Human disease

Ashes                          14                                Air pollution, Unsightliness

Feces                          1                                  Flies, human diseases

Public Health and Ecological Aspects

The proper storage at the point of generation, collection and disposal of the solid waste is part of the environmental health service program, which must be accomplished effectively in a community.

1. They produce a good breeding place for flies; hence create a favorable conditions for food contamination by flies and other fly-borne diseases.
2. Provide food and shelter for rats and mice, which are destroyers and contaminants of food and other goods.
3. Under certain conditions, may create suitable breeding place for mosquitoes. Subsequently bring in the problem of mosquito-borne diseases, (e.g. malaria, filariasis, etc)
4. May cause nuisances– which create aesthetic problem, (e.g. looks unpleasant and has bad smell, etc.)
5. May attract dogs, cats and other scavengers.
6. May cause fire hazards by instantaneous combustion.

The public health and ecological reasons for proper management of solid wastes are:

• An attractive media for the growth and multiplication of flies, and hence, may involve all diseases which are transmitted by flies, (e.g. typhoid fever, cholera, dysenteries. etc);
• A suitable breeding place for mosquitoes, subsequently bringing the problem of mosquito born diseases;
• A good harborage for rats, which can be an economic as well as health problem;
• From aesthetic point of view, such as bad odor, unsightly conditions etc;
• Pollution and contamination of air, land and water;
• Possible fire hazards by instantaneous combustion;